Should I file single or married filing separately if I have been living on my own for 10 years with no actual divorce paper?

[TTJGalSr]

Turbo Tax points to single but I am not sure?

[DoninGA]

If you are legally married and you have not been legally separated according to the laws of your state, then you can only file as Married Filing Jointly or Married Filing Separately.

Unless you have a qualifying person as a dependent you may be able to file as Head of Household.

[Opus 17 · Accepted solution]

If you are legally married, you must generally file as married (married filing separately) even if you have been separated for a long time.  Or if you provide care in your home for a qualifying dependent, you might qualify for head of household status.

There are a very limited number of situation where you might be "considered unmarried" and allowed to file as single, but this depends on the status of your separation under state law.  You would need to consult a tax attorney in your state if you think you might qualify.  The requirements for this status are fairly strict and difficult to meet.  At a minimum, you need a final order of separation from the family court that includes a final order of support or separate maintenance.  

[xmasbaby0]

What have you been doing for the past ten years?   If you are legally married your filing choices are to file married filing separately or married filing jointly.   Or ....if you have custody of qualified dependent children, you could file as Head of Household.   Living on your own with "no actual divorce papers" does not make you "Single"  if you have a legal spouse out there somewhere.